Enhanced efficiency fertilizer with urease inhibitor and nitrification inhibitor in separate particles

ABSTRACT

Particulate fertilizer compositions that include nitrification inhibitors and urease inhibitors are described herein. The inhibitors are separated from each other by being in separate particles. Fertilizer particles in the composition include particles having a core-shell structure, with an inhibitor included in the core particle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalPatent Application No. 62/487,260 filed Apr. 19, 2017, which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION A. Field of the Invention

The invention generally concerns fertilizer compositions that includeurease inhibitors and nitrification inhibitors. The urease andnitrification inhibitors are found in separate particles, and theparticles can include the inhibitor in a core that is surrounded by ashell of a nitrogen-containing fertilizer composition.

B. Description of Related Art

To increase crop yield and satisfy the growing needs of an increasingpopulation, more fertilizers are being used in agriculture. However,continuous use of fertilizer can lead to nutrient imbalance and loss ofsoil fertility. In addition, extensive use of urea fertilizer, due toits rapid hydrolysis and nitrification in the soil by soil bacteria, cancause deterioration of soil health and other environmental problems suchas greenhouse emissions and groundwater contamination.

Hydrolysis and nitrification of urea in soil can be counteracted byadding urease inhibitors and nitrification inhibitors to the fertilizer.Urease inhibitors reduce the amount of urea hydrolyzed, which reducesthe amount of nitrogen lost through ammonia volatilization.Nitrification inhibitors reduce the rate of conversion of ammonium intonitrate, which also reduces the amount of nitrogen lost. Nitrificationinhibitors are effective at enhancing efficiency of a variety ofnitrogen fertilizers in addition to urea.

While use of urease inhibitors and nitrification inhibitors infertilizers has been employed as a solution to the problems of ureahydrolysis and nitrification, there are certain difficulties in usingthese inhibitors. One problem is that some inhibitors are heatsensitive, which complicates the manufacturing process for fertilizersthat include such inhibitors. For example, adding a heat-sensitiveinhibitor to molten urea before granulation can cause substantialdegradation of the inhibitor, as described in Soil Use & Management,24:246 (2008). To compensate for this problem, some fertilizermanufacturers may add an excess of inhibitor to the urea melt, whichincreases the cost of producing the fertilizer. Another problem is thatsome combinations of inhibitors can be incompatible if included in thesame particle. For example, the inventors of the present applicationhave observed that the nitrification inhibitor dicyandiamide (DCD) cancause stability problems if combined with the urease inhibitorN-(n-butyl) thiophosphoric triamide (NBTPT). Without wishing to be boundby theory, it is commonly known that, under storage conditions, DCDincreases the degradation of NBTPT, which is both thermal as well asmoisture sensitive.

SUMMARY OF THE INVENTION

A solution to the aforementioned problems is disclosed below. In someembodiments, the solution resides in providing a particulate fertilizercomposition with two types of particles, each having a core-shellstructure: one type of particles has a nitrification inhibitor in thecore and another type of particles has a urease inhibitor in the core.This provides for a fertilizer composition in which the nitrificationinhibitor and urease inhibitor are physically separated from each other,thus preventing any degradation effects that the inhibitors can have oneach other and avoiding other issues with incompatible pairs ofinhibitors. The manufacturing process of the fertilizer compositionprovides protection against heat degradation for the inhibitors that areincluded in the core particles. This is accomplished by adding aninhibitor, for example DCD or NBTPT, to the core particle instead of toa relatively hot composition, such as molten urea, during the process ofmaking the fertilizer particles. The other ingredients in the coreparticle help provide a buffer against heat during the manufacturingprocess, reducing the amount of inhibitor lost to heat degradation. Inaddition, the manufacturing process of the fertilizer compositionsdisclosed herein can be simplified in that it is not necessary to makeparticles having both a nitrification inhibitor and a urease inhibitorin the same particle. Instead, separate core particles, each including adifferent inhibitor, can be prepared separately and then can be fattenedwith a nitrogen fertilizer-containing shell following the sameprocedure.

Disclosed herein is a particulate fertilizer composition that caninclude (a) a first particle that can include a first core particle anda first shell, wherein the first core particle can include a ureaseinhibitor and is substantially free of any nitrification inhibitors; and(b) a second particle that can contain a second core particle and asecond shell, wherein the second core particle can contain anitrification inhibitor and is substantially free of any ureaseinhibitor. The shells of each of the first particle and second particlecan contain a nitrogen-containing fertilizer composition such as, forexample, urea. The urease inhibitor in the first core particle cancontain a variety of inhibitors known in the art including, for example,N-(n-butyl) thiophosphoric triamide (NBTPT). The nitrification inhibitorin the second core particle can contain a variety of inhibitors known inthe art including, for example, dicyandiamide (DCD). This particulatefertilizer composition provides the advantage of keeping thenitrification and urease inhibitors in separate particles, thusmitigating incompatibilities between the inhibitors, such as thenegative effect of DCD on NBTPT stability.

The shell of the second particle (the “second shell”) can furthercontain a nitrification inhibitor. In such embodiments, both the secondcore particle and the second shell can contain a nitrificationinhibitor. Nitrification inhibitors, such as DCD, are particularlysuited to being included in a shell composition in addition to, orinstead of, in a core particle because during the manufacturing processthey can be added to a molten fertilizer composition, such as moltenurea, without suffering the same thermal degradation effects as someurease inhibitors, such as, for example, NBTPT.

The nitrification and urease inhibitors can be present in a range ofamounts. In some embodiments, the urease inhibitor is present in thefirst core particle in an amount between 1 and 5 wt % of the first coreparticle. The urease inhibitor can also be about 0.1, 0.5, 1.0, 1.5,2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 wt % of thecore particle or between any two of those values. In some embodiments,the nitrification inhibitor is present in the second core particle in anamount between about 10 and 50 wt % of the second core particle. Thenitrification inhibitor can also be about 0.1, 0.5, 0.6, 0.7, 0.8, 0.9,1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 3, 4, 5, 6, 7, 8,9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 wt % of the second coreparticle or between any two of those values. In embodiments in which thenitrification inhibitor is also included in the second shell, thenitrification inhibitor can also be about 0.1, 0.5, 0.6, 0.7, 0.8, 0.9,1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 3, 4, 5, 6, 7, 8,9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 wt % of the shell.

The amounts of nitrification and urease inhibitors included in therespective particles can be chosen such that the amounts in theparticulate fertilizer composition as a whole are effective to stabilizenitrogen in the soil to which the particulate fertilizer composition isapplied. That is, if the particulate fertilizer composition containsequal amounts of first and second particles, the amounts of inhibitorsin the respective particles would be double the amount that wouldnormally be used in a composition that included only one type ofparticle. For example, in such a composition having equal amounts offirst and second particles, if the desired final amount of ureaseinhibitor in a particulate fertilizer composition as a whole was 0.1 wt%, the amount of urease inhibitor in the first particles would be 0.2 wt% of the first particle (the amount as a percentage of the first coreparticle would be higher than this, given that the first core particleis only a portion of the first particle). The same would apply withregard to the amounts of nitrification inhibitors.

In some embodiments, the first core particle and second core particlecan contain substances in addition to the urease inhibitor and thebinder, such as a filler, a pH balancing agent, and a polymer thickener.The first core particles and second core particles can have differentamounts of these additional ingredients as needed to accommodatediffering amounts of inhibitor and to provide different desiredproperties.

A binder in the first core particle and/or second core particle can helpto keep the core particle from breaking or crumbling during themanufacturing process or storage. In some embodiments, the binder can beone or more of plaster of Paris, flour, biodegradable bleached wheatflour, starch, gluten, kaolin, bentonite, or colloidal silica, includingmixtures thereof. Other suitable binders known in the art can also beused. In some embodiments, the binder is present in the core particle inan amount between 10 and 99 wt % of the core particle. In someembodiments, the binder is present in the core particle in an amount ofabout 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, 98, or 99 wt % of the core particle or between any two of thosevalues.

In some embodiments, the filler in the first core particle and/or secondcore particle can contain one or more of silica, dried distillers grainswith solubles (DDGS), or rice husk, or mixtures thereof. Other suitablefillers known in the art can also be used. In some embodiments, thefiller is present in the core particle in an amount between greater than0 and 60 wt % of the core particle. In some embodiments, the filler ispresent in the core particle in an amount of about 1, 5, 10, 15, 20, 25,30, 35, 40, 45, 50, 55, or 60 wt % of the core particle or between anytwo of those values.

In some embodiments, the pH buffering agent in the first core particleand/or second core particle can be one or more of chalk powder, CaCO₃,Na₂CO₃, K₂CO₃, MgO, KH₂PO₄, NaHCO₃, or MgCO₃ or mixtures thereof. Insome embodiments, the filler is present in the core particle in anamount between about 5 and 60 wt % of the core particle. In someembodiments, the filler is present in the core particle in an amount ofabout 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 wt % of the coreparticle or between any two of those values. In some embodiments, a pHbuffering agent can also function as a filler. For example, in someembodiments, CaCO₃ is used as both the filler and as the pH bufferingagent, and no other fillers or pH buffering agents are included in thecore particle.

In some embodiments, the polymer thickener in the first core particleand/or second core particle can be one or more of hydroxypropylmethylcellulose, carboxymethylcellulose, hydroxyethylcellulose,polyethylene glycol (PEG), guar gum, locust bean gum, xanthan gum, othernatural gums, or synthetic polymers based on acrylates, polyacrylamide(PAM), PVP, or combinations of synthetic polymers and carbomers. In someembodiments, the polymer thickener is present in an amount between 0.1and 1 wt % of the core particle. In some embodiments, the polymerthickener is present in an amount of about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6,0.7, 0.8, 0.9, or 10 wt % of the core particle or between any two ofthose values.

The particulate fertilizer composition can contain a plurality of firstparticles and a plurality of second particles, in varying proportions.For example, the weight ratio of first particles to second particles canbe approximately 1:1. The weight ratio of first particles to secondparticles can also be approximately 1:5, 2:5, 3:5, 4:5, 1:1, 5:4, 5:3,5:2, or 5:1, or between any two of these values. The relative amounts ofinhibitors in the first and second particles can be adjusted based onthe weight ratio of the particles. For example, if the weight ratio offirst particles to second particles were 1:5, the amount of ureaseinhibitor in the first particles can be 5×, or five times the desiredfinal concentration (“1×”) in the fertilizer composition as a whole.

In some embodiments, the first core particle can contain the followingingredients in the indicated amounts, with the amounts being given asthe percent of the ingredient by weight in relation to the coreparticle: 10 to 94 wt % binder, 0 to 60 wt % filler, 5 to 60 wt % pHbalancing agent, and 1 to 5 wt % NBTPT. In some embodiments, the secondcore particle can contain the following ingredients in the indicatedamounts, with the amounts being given as the percent of the ingredientby weight in relation to the core particle: 10 to 85 wt % binder, 0 to50 wt % filler, 5 to 60 wt % pH balancing agent, and 10 to 50 wt % DCD.

Embodiments of the particles disclosed herein can include a variety ofdifferent arrangements and proportions of the core particles and theshells. For all disclosed dimensions, the first particle and secondparticle can have the same or different measurements. In someembodiments, there are multiple core particles in a single fertilizerparticle. In some embodiments, the diameter of the first core particleand/or second core particle is between about 0.5 and 2 mm. In someembodiments, the diameter of the core particle is about 0.1, 0.2, 0.3,0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7,1.8, 1.9, 2.0, 3.0, 4.0, or 5.0 mm or is between any two of thosevalues. In some embodiments, the thickness of the first shell and/orsecond shell is between about 1 and 6 mm. In some embodiments, thethickness of the shell is about 0.5, 0.6, 0.7, 0.8. 0.9, 1.0, 1.1, 1.2,1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 3.0, 4.0, 5.0, or 6.0 mm or isbetween any two of those values. In some embodiments, the shell is asolid nitrogen fertilizer-containing composition that has been formed byspraying the nitrogen fertilizer-containing composition in molten formonto the core particle and allowing the molten nitrogenfertilizer-containing composition to cool and solidify. In someembodiments, the molten nitrogen fertilizer-containing composition is amolten urea-containing composition. In some embodiments, the weightratio of the first shell or second shell to the first core particle orsecond core particle is about 2:1, 3:1, 4:1, 5:1, 10:1, 15:1, 20:1,30:1, 40:1, or 50:1 or is between any two of those values. In someembodiments, the first shell and/or second shell makes up about 70, 80,90, 95, or 99% of the weight of the first fertilizer particle and orsecond fertilizer particle or between any two of those values. In someembodiments, the first particle and/or second particle—including boththe core particle and shell—has a diameter of between 0.5 and 8 mm. Insome embodiments, the fertilizer particle has a diameter of about 0.2,0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 6.0, 7.0, 8.0, 9.0, or10.0 mm or between any two of those values. In some embodiments, thecore particle is an extruded particle. In some embodiments, the firstshell and/or second shell substantially or fully surrounds first coreparticle and/or the second core particle. In some embodiments, the shellcovers at least 90, 95, or 99% of the surface of the core particle. Inembodiments in which the shell fully surrounds the core particle, theshell covers 100% of the surface of the core particle.

Embodiments of the particulate fertilizer compositions disclosed hereincan be characterized by the stability of the nitrogen in the particleswhen exposed to soils. Because of the efficient distribution of ureaseinhibitors and nitrification inhibitors in separate particles, theparticulate fertilizer compositions described herein suffer less loss ofnitrogen due to hydrolysis and nitrification than would otherwise occur.In some embodiments, less than 20 wt % of the nitrogen in theparticulate fertilizer composition is lost via ammonia volatilizationafter being exposed to Greenville soil for 20 days. In some embodiments,the amount of nitrogen in the particulate fertilizer composition lostvia ammonia volatilization after being exposed to Greenville soil for 20days is less than 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18,17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 wt % or isbetween any two of those values. In some embodiments, less than 20 wt %of the nitrogen in the particulate fertilizer composition is lost afterbeing exposed to Crowley soil for 20 days. In some embodiments, theamount of nitrogen in the particulate fertilizer composition lost afterbeing exposed to Crowley soil for 20 days is less than 30, 29, 28, 27,26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9,8, 7, 6, 5, 4, 3, 2, or 1 wt % or is between any two of those values.

Also disclosed is a particulate fertilizer composition that can includeat least two of the following types of particles: (a) a plurality offirst particles, each first particle can include (i) a first coreparticle that can includes a urease inhibitor and a binder and (ii) aurea-containing fertilizer composition in contact with the outer surfaceof the first core particle; (b) a plurality of second particles, eachsecond particle can contain (i) a second core particle that can includea nitrification inhibitor and a binder and (ii) a urea-containingfertilizer composition in contact with the outer surface of the secondcore particle; and (c) a plurality of third particles, each thirdparticle can contain a urea-containing fertilizer and not contain a coreparticle. In some embodiments, each of the first particles aresubstantially free of any nitrification inhibitor, each of the secondparticles are substantially free of any urease inhibitor, and each ofthe third particles are substantially free of any nitrificationinhibitor or urease inhibitor. In some embodiments, each of the thirdparticles can further contain a nitrification inhibitor. In someembodiments, the urea-containing fertilizer composition in contact withthe outer surface of the second core particle can further contain DCD.This particulate fertilizer composition provides flexibility in making aparticulate fertilizer composition with the desired final concentrationsof inhibitors. For example, if a particulate fertilizer compositioncontains a 1× concentration of urease inhibitor and no nitrificationinhibitor, first particles with a 2× concentration of urease inhibitorcan be combined with third particles containing no inhibitor of any kindin a weight ratio of approximately 1:1. That would eliminate the needfor producing first core particles having varying concentrations ofurease inhibitor, allowing the final concentration of urease inhibitorin the final particulate fertilizer composition to be adjusted by addingan appropriate amount of third particles having no inhibitor. The samewould be true for producing particulate fertilizer compositions having adesired amount of nitrification inhibitors. In addition, a particulatefertilizer composition could include first particles with a 2×concentration of urease inhibitor mixed with an approximately equalamount of third particles with a 2× concentration of nitrificationinhibitor to result in a particulate fertilizer composition having a 1×concentration of both inhibitors. This would eliminate the need toproduce core-shell particles having nitrification inhibitors, which cansimplify the manufacturing process since some nitrification inhibitors,including DCD, are relatively heat-stable and can be added directly tomolten urea during the manufacturing process rather than having to beprotected within a core particle. Thus, a variety of combinations ofmixtures of the particles can be created. For example, the particulatefertilizer composition can include a plurality of the first particlesand a plurality of the second particles in a weight ratio ofapproximately 1:1, without including any third particles. As anotherexample, the particulate fertilizer composition can include a pluralityof the third particles and either a plurality of the first particles ora plurality of the second particles, with a weight ratio of firstparticles to second particles or third particles of approximately 1:1.In some embodiments, the plurality of third particles has an averagediameter of at least about 0.1, 0.2, 0.3, 0.4, or 0.5 mm.

Also disclosed is a method of enhancing plant growth by applying to soilan effective amount of a composition containing any of the particulatefertilizer compositions described herein.

Also disclosed are the following Embodiments 1 to 20 of the presentinvention. Embodiment 1 is a particulate fertilizer compositioncomprising: (a) a first particle comprising a first core particle and afirst shell, wherein the first core particle comprises a ureaseinhibitor and is substantially free of any nitrification inhibitor; and(b) a second particle comprising a second core particle and a secondshell, wherein the second core particle comprises a nitrificationinhibitor and is substantially free of any urease inhibitor. Embodiment2 is the particulate fertilizer composition of Embodiment 1, wherein thefirst shell and the second shell comprise a nitrogen-containingfertilizer composition. Embodiment 3 is the particulate fertilizercomposition of Embodiment 1 or 2, wherein the second shell furthercomprises a nitrification inhibitor. Embodiment 4 is the particulatefertilizer composition of any one of Embodiments 1 to 3, wherein theurease inhibitor comprises N-(n-butyl) thiophosphoric triamide (NBTPT)and the nitrification inhibitor comprises dicyandiamide (DCD).Embodiment 5 is the particulate fertilizer composition of any one ofEmbodiments 1 to 4, wherein the first core particle comprises NBTPT andthe NBTPT is between 1 and 5 wt % of the first core particle and thesecond core particle comprises DCD and the DCD is between 10 and 50 wt %of the second core particle. Embodiment 6 is the particulate fertilizercomposition of any one of Embodiments 1 to 5, wherein the first coreparticle and the second core particle further comprise a bindercomprising one or more of plaster of Paris, flour, biodegradablebleached wheat flour, starch, colloidal silica, kaolin, bentonite, orgluten. Embodiment 7 is the particulate fertilizer composition of anyone of Embodiments 1 to 6, wherein the first core particle and thesecond core particle further comprise a filler comprising one or more ofsilica, dried distillers grains with solubles (DDGS), or rice husk.Embodiment 8 is the particulate fertilizer composition of any one ofEmbodiments 1 to 7, wherein the first core particle and the second coreparticle further comprise a pH buffering agent comprising one or more ofchalk powder, CaCO₃, MgO, KH₂PO₄, NaHCO₃, Na₂CO₃, or K₂CO₃. Embodiment 9is the particulate fertilizer composition of any one of Embodiments 1 to8, wherein the particulate fertilizer composition comprises a pluralityof first particles and a plurality of second particles, and wherein theweight ratio of the first particles to the second particles isapproximately 1:1. Embodiment 10 is the particulate fertilizercomposition of any one of Embodiments 1 to 9, wherein the first coreparticle comprises 10 to 94 wt % binder, 0 to 60 wt % filler, 5 to 60 wt% pH balancing agent, and 1 to 5 wt % NBTPT, and wherein the second coreparticle comprises 10 to 85 wt % binder, 0 to 50 wt % filler, 5 to 60 wt% pH balancing agent, and 10 to 50 wt % DCD. Embodiment 11 is theparticulate fertilizer composition of any one of Embodiments 1 to 10,wherein the weight ratio of the first shell to the first core particleand of the second shell to the second core particle is between about40:1 and 5:1. Embodiment 12 is the particulate fertilizer composition ofany one of Embodiments 1 to 11, wherein the first core particle andsecond core particle are between about 0.5 and 2 mm in diameter andwherein the first particle and the second particle are between about 1and 8 mm in diameter. Embodiment 13 is the particulate fertilizercomposition of any one of Embodiments 1 to 12, wherein the particulatefertilizer composition comprises nitrogen and less than 20 wt % of thenitrogen in the particulate fertilizer composition is lost via ammoniavolatilization after being exposed to Greenville soil or Crowley soilfor 20 days. Embodiment 14 is a particulate fertilizer compositioncomprising at least two of the following groups of particles: (a) aplurality of first particles, each first particle comprising: (i) afirst core particle comprising NBTPT and a binder; and (ii) aurea-containing fertilizer composition in contact with the outer surfaceof the first core particle; and (b) a plurality of second particles,each second particle comprising: (i) a second core particle comprisingDCD and a binder; and (ii) a urea-containing fertilizer composition incontact with the outer surface of the second core particle; and (c) aplurality of third particles, each third particle comprising aurea-containing fertilizer and not comprising a core particle.Embodiment 15 is the particulate fertilizer composition of Embodiment14, wherein each of the first particles are substantially free of anynitrification inhibitor, each of the second particles are substantiallyfree of any urease inhibitor, and each of the third particles aresubstantially free of any nitrification inhibitor or urease inhibitor.Embodiment 16 is the particulate fertilizer composition of Embodiment14, wherein each of the third particles further comprise a nitrificationinhibitor. Embodiment 17 is the particulate fertilizer composition ofany one of Embodiments 14 to 16, wherein the urea-containing fertilizercomposition in contact with the outer surface of the second coreparticle further comprises DCD. Embodiment 18 is the particulatefertilizer composition of any one of Embodiments 14 to 17, wherein thethird particle has a diameter of at least 0.5 mm. Embodiment 19 is theparticulate fertilizer composition of any one of Embodiments 14 to 18,wherein the particulate fertilizer composition comprises a plurality ofthe first particles and a plurality of the second particles, wherein theparticulate fertilizer does not comprise the third particle, and whereinthe weight ratio of the first particles to the second particles isapproximately 1:1. Embodiment 20 is the particulate fertilizercomposition of any one of Embodiments 14 to 17, wherein the particulatefertilizer composition comprises a plurality of the third particles andeither a plurality of the first particles or a plurality of the secondparticles, and wherein the weight ratio of the third particles to thefirst particles or the second particles is approximately 1:1.

The terms “about” or “approximately” as used herein are defined as beingclose to as understood by one of ordinary skill in the art. In onenon-limiting embodiment, the terms are defined to be within 10%,preferably within 5%, more preferably within 1%, and most preferablywithin 0.5%.

The terms “wt %”, “vol. %”, or “mol. %” refers to a weight, volume, ormolar percentage of a component, respectively, based on the totalweight, the total volume of material, or total moles, that includes thecomponent. In a non-limiting example, 10 grams of component in 100 gramsof the material is 10 wt % of component.

The term “substantially” and its variations are defined to includeranges within 10%, within 5%, within 1%, or within 0.5%.

The terms “inhibiting” or “reducing” or “preventing” or “avoiding” orany variation of these terms, when used in the claims and/or thespecification includes any measurable decrease or complete inhibition toachieve a desired result.

The term “effective,” as that term is used in the specification and/orclaims, means adequate to accomplish a desired, expected, or intendedresult.

The use of the words “a” or “an” when used in conjunction with any ofthe terms “comprising,” “including,” “containing,” or “having” in theclaims, or the specification, can mean “one,” but it is also consistentwith the meaning of “one or more,” “at least one,” and “one or more thanone.”

The words “comprising” (and any form of comprising, such as “comprise”and “comprises”), “having” (and any form of having, such as “have” and“has”), “including” (and any form of including, such as “includes” and“include”) or “containing” (and any form of containing, such as“contains” and “contain”) are inclusive or open-ended and do not excludeadditional, unrecited elements or method steps.

The fertilizer compositions of the present invention can “comprise,”“consist essentially of,” or “consist of” particular ingredients,components, compositions, etc. disclosed throughout the specification.With respect to the transitional phrase “consisting essentially of,” inone non-limiting aspect, a basic and novel characteristic of thefertilizer particles compositions of the present invention are theirabilities to inhibit degradation of the components contained therein.

Other objects, features and advantages of the present invention willbecome apparent from the following figures, detailed description, andexamples. It should be understood, however, that the figures, detaileddescription, and examples, while indicating specific embodiments of theinvention, are given by way of illustration only and are not meant to belimiting. Additionally, it is contemplated that changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description. Infurther embodiments, features from specific embodiments can be combinedwith features from other embodiments. For example, features from oneembodiment can be combined with features from any of the otherembodiments. In further embodiments, additional features can be added tothe specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention can become apparent to those skilledin the art with the benefit of the following detailed description andupon reference to the accompanying drawings. While the invention issusceptible to various modifications and alternative forms, specificembodiments thereof are shown by way of example in the drawings. Thedrawings may not be to scale.

FIGS. 1A and 1B illustrate cross sections of fertilizer particles. FIG.1A shows a cross section of a core-shell fertilizer particle. FIG. 1Bshows a cross section of a homogeneous fertilizer particle.

FIG. 2 depicts an embodiment of a process by which a core-shellfertilizer particle is produced.

DETAILED DESCRIPTION OF THE INVENTION

Particulate fertilizer compositions described herein are a mixture of atleast two different types of fertilizer particles. Some of thefertilizer particles described herein can contain two discrete portions:a core particle and a shell of a nitrogen-based fertilizer composition.Other fertilizer particles are homogeneous, containing a single matrixof a nitrogen-based fertilizer composition with, in some embodiments,additional ingredients like nitrification inhibitors distributedthroughout that matrix. These and other non-limiting aspects of thepresent invention are discussed in further detail in the followingsections.

A. Fertilizer Particle

An illustrative cross section view of an embodiment of a core-shellfertilizer particle for use in the particulate fertilizer compositionsof the invention is depicted in FIG. 1A. In the illustrated embodiment,the fertilizer particle 10 can contain a core particle 2 and a shell 4.The core particle 2 has a circular cross-section, although other shapescan readily be made. The core particle 2 can contain a nitrificationinhibitor or urease inhibitor and additional ingredients including, forexample, a binder. The core particle 2 can also contain a filler, a pHbalancing agent, and/or a polymer thickener. In the illustratedembodiment, a shell 4 surrounding the core particle 2 is made from asolid urea-containing composition. It is particularly advantageous tohave the urease inhibitor NBTPT in the core particle 2, as this canprotect that NBTPT from thermal degradation during the granulationprocess. It will be apparent to persons of ordinary skill in the artthat a variety of configurations of the fertilizer particle 10 arepossible. For example, a particle can be made that has nitrificationinhibitor in both the core particle 2 and in the shell 4.

An illustrative cross section view of an embodiment of a homogeneousfertilizer particle is depicted in FIG. 1B. The homogeneous fertilizerparticle 20 can contain a matrix 22 of a nitrogen fertilizer-containingcomposition, such as solid urea. The homogeneous fertilizer particle 20can also contain an inhibitor, such as DCD, and other suitableingredients such as binders, pH balancing agents, and/or fillersdistributed within the matrix 22.

Particulate fertilizer compositions can include combinations ofdifferent types of core-shell particles. For example, a particulatefertilizer composition can include a mixture of particles that haveNBTPT in the core particle and particles that have DCD in the coreparticle. Either of these types of particles can be mixed withhomogeneous fertilizer particles that contain no inhibitor.

While the fertilizer particles illustrated in FIGS. 1A and 1B havecircular cross-sections, a variety of shapes are possible. For example,the fertilizer particle can have a spherical, puck, oval, or oblongshape. The fertilizer particles can also have a variety of sizes. Insome embodiments, the fertilizer particle has a longest dimensionbetween about 1 and 8 mm.

Binders to be used in the fertilizer particle can be chosen for theirsuitability to extrusion processes for making core particles. In someinstances, the binders are receptive to a solvent, such as, for example,water. “Receptive to solvents” in this context means that the solventswill affect the binding properties of the binder. Accordingly, asdescribed herein, an appropriate solvent will affect the bindingproperties of a particular binder, as well as other binders, fillers,and excipients in the formulation.

Core particles and fertilizer particles disclosed herein have desirablephysical properties such as desired levels of abrasion resistance,particle strength, pelletizability, hygroscopicity, particle shape, andsize distribution, which are important properties for the fertilizercore particle. Accordingly, the binder can be chosen to optimize theseproperties.

A particular application of embodiments disclosed herein is thestabilization of an inhibitor, such as, for example, NBTPT present inthe core particle and of other fertilizer additives. Certain fertilizeradditives are unstable and tend to degrade upon exposure to hightemperatures, changes in pH (either acidic or basic), etc. In particularinstances, fertilizer core particles disclosed herein are embeddedwithin or coated with a fertilizer composition such as, for example,urea. In some instances, a shell that can contain urea substantiallysurrounds at least a portion of the outer surface of the core particle.

In conventional fertilizer technology, various fertilizer additives aremixed with a fertilizer using an “all in one” methodology. In theseinstances, fertilizers, fertilizer additives, excipients, and otheringredients are mixed together to form a fertilizer composition in theform of particles or granules. In most cases, granulation is performedat elevated temperatures such that the fertilizer composition is at amolten state. For example, the granulation temperature for molten ureais about 135° C. at about 35 atm pressure. Many fertilizer additivesdegrade, at least partially, under these conditions. Traditionally,these stability problems have been circumvented by using a large excessof fertilizer additives. Such methods, although in use, are sub-optimaland raise concerns regarding cost, efficacy, by-products, environmentalwaste, and green-house gases, etc.

The production of core particles disclosed herein provides a solution tothe instability of some fertilizer additives at higher temperatures. Thebinder, pH stabilizing agent and/or filler can be chosen such that theresulting composition synergistically protects the fertilizer additivesfrom high temperature degradation. As disclosed herein, the binder, pHstabilizing agent, filler, and polymer thickener can be mixed togetherwith the fertilizer additive and extruded to form a core particle.

In some embodiments, no nitrogen fertilizer composition is present inthe core particle. Thus, in such instances, only the fertilizeradditive, such as a urease inhibitor or nitrification inhibitor(together with the binder, pH buffering agent, and/or filler) is presentin within the core particle.

Some of the fertilizer additives are unstable towards changes in pH,either in the composition during the manufacturing process, or afterapplication to the soil. For example, in the case of nitrogen containingfertilizers, after application, the soil environment becomes acidic.Accordingly, fertilizer additives that are sensitive to the acidic pHdegrade and will not reach their full performance capability. Includinga large excess of fertilizer additives to compensate for the loss due topH variations may not be successful, since the fertilizers, which arepresent in a large excess (in comparison to the fertilizer additives),continue to alter the pH of the soil environment. Also, some commercialproducts, such as SUPERU®, use organic solvents like NMP for addingfertilizer additives to the fertilizer composition. Such use isundesired and is avoided in the production of certain embodiments of thefertilizer particles described herein.

In some embodiments disclosed herein, the core particle is embeddedwithin a nitrogen fertilizer-containing composition, including aurea-containing composition. For example, in some embodiments, a shellcontaining a fertilizer composition at least partially surrounds theouter surface of the fertilizer core particle. In some of theseembodiments, the shell can contain a nitrogen containing fertilizercomposition, such as urea. In some instances, two or more core particlescan be embedded within a urea matrix.

B. Urease Inhibitors and Nitrification Inhibitors

Urea is one of the most widely used fertilizers because of its highnitrogen content (46.6%). A number of urease and nitrificationinhibitors have been developed to enhance the efficiency of ureafertilizer, but their application can be challenging due to stabilityproblems in the soil under various conditions such as pH, temperature,precipitation, etc. For example, NBTPT is known to be a good inhibitorof urease but it is unstable under acidic pH. NBTPT also decomposes whenexposed to high temperatures, such as the temperature of a urea melt(about 135-140° C.).

To overcome these issues, embodiments of the fertilizer particle areprovided that contain a core particle that is coated with an outercoating of urea that will first come in contact with the soil,protecting the active ingredients in the core particle, which will getreleased gradually. The fertilizer core particle can contain both abinder and a pH buffering agent. The pH buffering agent, for exampleCaCO₃, which can be provided in the form of chalk powder, is a materialthat can neutralize the acidity caused by urea hydrolysis, therebypreventing active agents, such as, for example, NBTPT, from degradingwhen placed in soil with an acidic pH. Thus, the pH buffering agent canincrease the efficacy of active agents, such as, for example, NBTPT, andalso maintains soil pH. The fertilizer particles also have the advantageof keeping a urease inhibitor and a nitrification inhibitor in separateareas of the fertilizer particle, which prevents any degradation orother detrimental effects from combining different inhibitors.

The binder in the fertilizer core particle protects the activeingredient, for example NBTPT, from being exposed to high temperaturesduring the granulation process, thereby preventing NBTPT fromdecomposing in the granulation process. For example, plaster of Paris(PoP)-containing cores can prevent NBTPT degradation efficiently duringthe granulation process. In such a formulation, all active ingredientsare protected inside the core by the PoP.

Additional inhibitors besides NBTPT and DCD can be included in thefertilizer particles described herein, including without limitation,3,4-dimethylpyrazole phosphate (DMPP), thio-urea (TU), phenylphosphorodiamidate (PPDA), 2-Chloro-6-(trichloromethyl)-pyridine(Nitrapyrin), 5-Ethoxy-3-trichloromethyl-1,2,4-thiadiazol (Terrazole),2-Amino-4-chloro-6-methyl-pyrimidine (AM), 2-Mercapto-benzothiazole(MBT), or 2-Sulfanimalamidothiazole (ST), or combinations thereof.

Additional fertilizer substances besides urea can be included in thefertilizer particles. Additional fertilizers can be chosen based on theparticular needs of certain types of soil, climate, or other growingconditions to maximize the efficacy of the fertilizer particle inenhancing plant growth and crop yield. Additional additives can also beincluded in the fertilizer particles, including without limitationmicronutrients, primary nutrients, and secondary nutrients. Amicronutrient is a botanically acceptable form of an inorganic ororganometallic compound such as boron, copper, iron, chloride,manganese, molybdenum, nickel, or zinc. A primary nutrient is a materialthat can deliver nitrogen, phosphorous, and/or potassium to a plant.Nitrogen-containing primary nutrients can include urea, ammoniumnitrate, ammonium sulfate, diammonium phosphate, monoammonium phosphate,urea-formaldehyde, or combinations thereof. A secondary nutrient is asubstance that can deliver calcium, magnesium, and/or sulfur to a plant.Secondary nutrients can include lime, gypsum, superphosphate, or acombination thereof.

C. Binders

The fertilizer particles described herein can contain a binder, which isa material that is used to bind together components in a mixture throughadhesive and/or cohesive forces. The core particle can contain from 10to 99 wt % of binder. The amount and type of binder can be chosen basedon the desired final properties of the core particle. The binder can beselected so that an extrusion process can be used during the productionof the core particle. It is understood that for some binders, such asplaster of Paris and bleached wheat flour, an amount of water (moisture)is needed to make the core extrudable. Any free moisture content presentin the core material during the extrusion process is typically removedpost-extrusion. However, residual amounts of free moisture content,typically below 4 wt %, such as, for example, below 0.5 wt %, can bepresent in the core particle.

In one aspect, the binder can contain a phosphate, a polyphosphate, abiodegradable polymer, or a wax, or a combination thereof. Suitablewaxes can include, but are not limited to, vegetable waxes, high meltwaxes, ethylene bis(stearamide) wax, paraffin waxes, polyethylene basedwaxes, and olefin waxes. Suitable phosphates can include, but are notlimited to, diammonium phosphate, and monoammonium phosphate. Suitablepolyphosphates can include, but are not limited to, ammoniumpolyphosphate. Suitable biodegradable polymers can include, but are notlimited to, polyacrylamide, polyacrylic acid, polyacrylonitrile,biodegradable polylactic acid and other biodegradable polymeric materialsuch as polylactic acid, poly(3-hydroxypropionic acid), polyvinylalcohol, poly e-caprolactone, poly L-lactide, polybutylene succinate,and biodegradable starch based polymers.

In another aspect, the binder can contain plaster of Paris, flour,starch, gluten, kaolin, bentonite, colloidal silica, or combinationsthereof. Suitable flours can include, but are not limited to, riceflour, wheat flour, and bleached wheat flour. Suitable starches caninclude, but are not limited to, dextrin modified starches.

D. pH Buffering Agents

The core particle can also contain one or more pH buffering agents tohelp counteract the tendency of urea fertilizer to acidify the soil.Examples of suitable pH buffering agents can include, but are notlimited to, CaCO₃, MgO, KH₂PO₄, NaHCO₃, chalk powder, aluminum,magnesium hydroxide, aluminum hydroxide/magnesium hydroxideco-precipitate, aluminum hydroxide/sodium bicarbonate co-precipitate,calcium acetate, calcium bicarbonate, calcium borate, calcium carbonate,calcium bicarbonate, calcium citrate, calcium gluconate, calciumhydroxide, dibasic sodium phosphate, dipotassium hydrogen phosphate,dipotassium phosphate, disodium hydrogen phosphate, magnesium acetate,magnesium borate, magnesium bicarbonate, magnesium carbonate, magnesiumhydroxide, magnesium lactate, magnesium oxide, magnesium phosphate,magnesium silicate, magnesium succinate, magnesium tartrate, potassiumacetate, potassium carbonate, potassium bicarbonate, potassium borate,potassium citrate, potassium metaphosphate, potassium phthalate,potassium phosphate, potassium polyphosphate, potassium pyrophosphate,potassium succinate, potassium tartrate, sodium acetate, sodiumbicarbonate, sodium borate, sodium carbonate, sodium citrate, sodiumgluconate, sodium hydrogen phosphate, sodium hydroxide, sodium lactate,sodium phthalate, sodium phosphate, sodium polyphosphate, sodiumpyrophosphate, sodium tartrate, sodium tripolyphosphate, synthetichydrotalcite, tetrapotassium pyrophosphate, tetrasodium pyrophosphate,tripotassium phosphate, trisodium phosphate, and trometamol, andcombinations thereof.

E. Fillers

The core particles in the fertilizer particles can contain a filler,which is a material that can improve the physical properties of the coreparticle, such as crush strength, homogeneity, and extrusion properties,or alter the release kinetics of inhibitors or micronutrients from thecore particle. A filler in combination with a binder can be selected toenhance physical and release properties of the core particle. The fillercan contain, for example, silica, dried distillers grains with solubles(DDGS), rice husk or other biomaterial, or a combination thereof.

F. Nitrogen Fertilizer-Containing Composition

In one aspect, the fertilizer particle can contain an outer layer, orshell, containing a nitrogen fertilizer, such as urea or a combinationof urea with other nitrogen fertilizers. Suitable other nitrogenfertilizers can include, but are not limited to, ammonium nitrate,ammonium sulfate, DAP, MAP, urea-formaldehyde, ammonium chloride, andpotassium nitrate. A urea-containing shell can be fattened onto the coreparticle by spraying molten urea onto the core particle in a granulationprocess.

G. Compositions

The particulate fertilizer compositions described herein can themselvesbe used for application to soil or can be mixed with other components ina composition useful for application to soil. In addition to thefertilizer particles, the composition can include other fertilizercompounds, micronutrients, primary nutrients, secondary nutrients,insecticides, herbicides, fungicides, and combinations thereof.

The particulate fertilizer compositions described herein can also beincluded in a blended composition containing other fertilizer granules.The other fertilizer granules can be granules of urea, Single SuperPhosphate (SSP), Triple Super Phosphate (TSP), ammonium sulfate and thelike.

H. Method of Making Fertilizer Particles and Particulate FertilizerCompositions

In some embodiments, core particles used in the core-shell particles aremade by extruding a composition containing a urease inhibitor, a binder,and, optionally, other suitable substances such as fillers, pH balancingagents, or other additives. The composition can be formed by mixing theingredients in dry form, adding any solvent, if needed, and furthermixing to make an extrudable composition. A solvent, such as water, maybe needed to make an extrudable composition if the binder is plaster ofParis, flour, starch, or gluten, but may not be needed if the bindercontains a wax. The extrusion can be done using suitable extruderapparatus known in the art and can be performed at a temperature between0° C. and 150° C. and a screw speed from 1 to 500 rpm, wherein theextruder can contain a multi-feeder containing extrusion components thatcan include a main drive, shaft, screw, barrel, and/or die. In someembodiments, the binder can be plaster of Paris, and the extrusion isperformed at a temperature between about 15° C. and 50° C. In someembodiments, the extrusion method can include slicing the extrudate,forming a core particle having a cylindrical shape and having both adiameter and a length between about 0.5 and 2.0 mm. The method can alsoinclude a drying step to remove solvent that may have been added to makethe composition extrudable. The cylindrical core particle can bespheronized, producing a core particle having a substantially sphericalshape.

The core particle can be fattened with a shell containing aurea-containing composition, thereby forming a fertilizer particle. Thefattening process can include spraying a molten urea-containingcomposition onto the core particle, for example, in a granulationapparatus known in the art. As the molten urea-containing composition issprayed onto the core particle, it cools and solidifies, resulting in afertilizer particle. The resulting fertilizer particle can be of varioussizes. In some embodiments, the fertilizer particle has a size betweenabout 1 and 8 mm.

FIG. 2 illustrates an embodiment of a process by which a fertilizerparticle 10 can be produced. To make the core particle 2, the coreparticle ingredients, which can include a binder, filler, pH balancingagent, polymer thickener, and a urease inhibitor or nitrificationinhibitor, among other suitable ingredients, are placed into the hopperof an extruder 6. The extruder 6 pushes the mixed core particleingredients through a die 8 in the process of extrusion 12. Duringextrusion 12, a cutting implement (not shown) associated with the die 8cuts the extrudate into pieces, resulting in core particles 2 (not drawnto scale), which can be further processed (not shown) to be dried, ifneeded, and made spherical. The core particles are then added to agranulator 14. Molten urea, which can also include DCD, is deliveredinto the granulator apparatus through a pipe 16. Within the granulator14, the molten urea is sprayed onto the surface of the core particles 2,where it cools and solidifies in a process known as fattening 18. Afterfattening 18, the fertilizer particle 10 has both a core particle 2 anda solid urea-containing shell.

Particulate fertilizer compositions including two types of core-shellparticles can be made in a variety of ways. In one way, a core-shellparticle containing a urease inhibitor in the core particle can be madeand, separately, a core-shell particle containing a nitrificationinhibitor in the core particle can be made, and then the different typesof core-shell particles are mixed in the desired proportion to make aparticulate fertilizer composition containing both types of core-shellparticles. Another way of making such a composition would be toseparately prepare core particles having a urease inhibitor and coreparticles having a nitrification inhibitor. The core particles can thenbe mixed together in the desired proportions before being added to thegranulator and fattened. The result would be a mixture of core-shellparticles with urease inhibitor in the core and core-shell particleswith nitrification inhibitor in the core.

Homogeneous fertilizer particles to be included in the particulatefertilizer compositions described herein can be made according toconventional granulation or prilling techniques. In the case ofhomogeneous fertilizer particles that include DCD, the DCD can be addedin the desired amounts to the molten urea composition beforegranulation.

I. Methods of Using Fertilizer Particles

The particulate fertilizer compositions described herein can be used inmethods of increasing the amount of nitrogen in soil and of enhancingplant growth. Such methods can include applying to the soil an effectiveamount of a composition containing the fertilizer particles. The methodcan include increasing the growth and yield of crops such as, forexample, rice, wheat, corn, barley, oats, and soybeans.

The effectiveness of the particulate fertilizer compositions describedherein can be ascertained by measuring the amount of nitrogen in thesoil at various times after applying the fertilizer composition to thesoil. It is understood that different soils have differentcharacteristics, which can affect the stability of the nitrogen in thesoil. The effectiveness of a fertilizer composition can also be directlycompared to other fertilizer compositions by doing a side-by-sidecomparison in the same soil under the same conditions. Compositionscontaining the fertilizer particles described herein can be compareddirectly to such fertilizers as AGROTAIN® or SUPERU®. AGROTAIN® is soldby Koch Fertilizer, LLC (U.S.A.) and is an NBTPT-containing liquidformulation, with NMP as the main solvent along with other additives toallow for spreading of this liquid onto urea granules, generally at thefarm site. Thus, it requires an additional step before being used by thefarmer and incorporates the toxic solvent NMP. Tremendous odor isevident during usage. SUPERU® is sold by Koch Fertilizer, LLC and is aformulation of urea containing both NBTPT and DCD prepared by addingthese two inhibitors to the urea melt during granulation.

EXAMPLES

The present invention will be described in greater detail by way ofspecific examples. The following examples are offered for illustrativepurposes only, and are not intended to limit the invention in anymanner. Those of skill in the art will readily recognize a variety ofnoncritical parameters which can be changed or modified to yieldessentially the same results.

Example 1 Methods of Making Fertilizer Particles and Analyzing theirProperties A. Materials

Technical grade urea can be obtained from SABIC® (Kingdom of SaudiArabia). Plaster of Paris, chalk powder and bleached wheat flour wereobtained from Bengaluru local markets. Hydroxypropylmethylcellulose(HPMC) was bought from Loba Chemie Pvt. Ltd. N-(n-butyl) thiophosphorictriamide (NBTPT) was purchased from Samich (HK) Ltd., Hangzhou, China.DCD powder was purchased from Sigma Aldrich/AlzChem, Germany.

B. Procedure for Extruding Core Particles

Representative procedure for lab scale extruder: The raw materialsneeded for formulations are weighed to the nearest accuracy and mixedthoroughly. The compounding operations are carried out in a W &P ZSK25Twin Screw Extruder with a 25 mm screw diameter on a 6-barrel. The screwconfiguration is designed with sufficient kneading elements to getmaximum shear for better mixing. The experiments are carried out at aprocessing temperature ranging from 5° C. to 50° C. The temperature ofthe extrusion process can be controlled by the screw speed used in theextrusion process. Screw speed is between 20-100 rpm and the material isadded through the main hopper at 6-8 kg/hr. The temperature of theextrusion process for fertilizer core particles containing plaster ofParis is generally between 20° C. and 50° C. The ingredients are addedthrough the hopper slowly by keeping the load constant. The extrudatesare collected as strands and dried at room temperature.

C. Procedure for Coating Core Particles and Granulation

The extruded core particles with either NBTPT or DCD included areprovided as described above. Core particles having a longest dimensionof 0.7-1.7 mm are chosen for granulation. During the granulationprocess, active ingredients, such as the inhibitors, are protectedinside the core particles by the binder materials used in theformulation. The core particles are placed in the granulator, eithertogether or in separate batches. The core particles are sprayed with aurea melt, which can contain a nitrification inhibitor, inside thegranulator to produce the fertilizer particle. The granulated fertilizercore (fertilizer particles) generally have a longest dimension of about4 mm. The granulating process both fattens the cores with urea and driesthe fertilizer granules.

The spray rate of the urea melt can be controlled to control theagglomeration of multiple cores into one fertilizer granule. Round,single, and multi-core fertilizer granules can be produced using thisprocess.

The granulation process parameters that can be used are described inTable 1.

TABLE 1 Process Coating Bin Coating Bin Nozzle Bottom spray; Diameter1.2 mm, Air cap 2.6 mm Atomization air pressure 0.8 bar Distributionplate Sieve plate with 58% free area Sieve cloth 1×; 25 μm mesh sizeNozzle heating 160° C. (thermal oil temperature) Liquid tank heating150° C. (thermal oil temperature) Atomization air heating 100° C.Electrical trace heating (tube) 160° C. Valve I heating 160° C. (infront of the nozzle) Valve II heating 160° C. (liquid tank discharge)

Example 2 (Prophetic Example) Sample Analysis

The purity of NBTPT and DCD can be cross-checked by NMR, HPLC, and LCMSanalysis.

Crush strength can be measured for some of the samples using a crushstrength analyzer to determine the strength of the extrudates fertilizerparticles.

The stability of inhibitors in the urea melt, core particles, and/orfertilizer particles can be measured using HPLC and LCMS.

The free and total moisture content of extrudates can be measured usinga moisture analyzer.

It is expected that the final core-shell fertilizer particles will havethe following properties: crush strength (kgf): 1.68-3.60; abrasionanalysis (wt loss %): 0.11-0.85; impact resistance (shattered granules%): 0.05-0.64; moisture analysis (wt %): 0.12-0.23; particle sizedistribution (granule): 2-4 mm (97%); Biuret %: 1.05-3.8; and Nitrogen%: 43.3-46.3.

The nitrogen volatilization and nitrogen transformation (nitrification)will be measured in different soils and compared to urea alone and toproducts on the market such as AGROTAIN®, ESN®, and SUPERU®. A soil thatis representative of a broader class of soil types can be used tomeasure the nitrogen volatilization and nitrification. Greenville soiland Crowley soil are two such representative soils. Other soils can alsobe used for the experiments described herein.

Greenville soil or Greenville clay-loam soil is typical of weatheredtropical ultisols and is found in warm humid environments. The soil isclassified as fine, kaolinitic, thermic Rhodic Kandiudults with a pH of6.1-6. The soil has organic matter of 1.4%, total amount of nitrogen isabout 0.06%, and the CEC is 5.2 cmol/kg. Accordingly, the soil has a lowcontent of organic matter, and also low availability of sulfur andnitrogen. Thus, the soil is ideal for nitrogen and sulfur trials withfertilizers.

Crowley soil consists of very deep, somewhat poorly drained, very slowlypermeable soils that formed in clayey fluviomarine deposits of thePleistocene age. The soil exists in nearly level to very gently slopingsoils and occurs on flat coastal plains terraces. The slope isdominantly less than 1 percent but ranges to up to 3 percent. The meanannual precipitation is about 1549 mm (61 in.), and the mean annual airtemperature is about 20 degrees C. (68 degrees F.), where the soil isfound. The soil is fine, smectitic, and thermic Typic Albaqualfs.

The nitrogen volatilization of various exemplary samples of theparticulate fertilizer composition of the invention as compared toAGROTAIN®, ESN®, SUPERU®, and urea will be determined as the percentageof nitrogen loss via ammonia volatilization as compared to the amount ofnitrogen applied or as the absolute mass of nitrogen lost via ammoniavolatilization. It is expected that embodiments of the fertilizercomposition disclosed herein will lose less than 20 wt % of the appliednitrogen after being exposed to soil for 20 days. It is also expectedthat embodiments of the fertilizer composition disclosed herein willlose less than 20 wt % of the applied nitrogen after being exposed toGreenville soil for 20 days and less than 20 wt % of the appliednitrogen after being exposed to Crowley soil for 20 days. It is alsoexpected that embodiments of the fertilizer particles disclosed hereinwill have lower levels of ammonia volatilization and/or nitrogen lossthan AGROTAIN®, ESN®, and/or SUPERU® tested under substantiallyidentical conditions in a given soil, which can include Greenville soil,Crowley soil, or other soils.

1. A particulate fertilizer composition comprising: (a) a first particlecomprising a first core particle and a first shell, wherein the firstcore particle comprises a urease inhibitor and is substantially free ofany nitrification inhibitor; and (b) a second particle comprising asecond core particle and a second shell, wherein the second coreparticle comprises a nitrification inhibitor and is substantially freeof any urease inhibitor.
 2. The particulate fertilizer composition ofclaim 1, wherein the first shell and the second shell comprise anitrogen-containing fertilizer composition.
 3. The particulatefertilizer composition of claim 1, wherein the second shell furthercomprises a nitrification inhibitor.
 4. The particulate fertilizercomposition of claim 1, wherein the urease inhibitor comprisesN-(n-butyl) thiophosphoric triamide (NBTPT) and the nitrificationinhibitor comprises dicyandiamide (DCD).
 5. The particulate fertilizercomposition of claim 4, wherein the NBTPT is between 1 and 5 wt % of thefirst core particle and the DCD is between 10 and 50 wt % of the secondcore particle.
 6. The particulate fertilizer composition of claim 1,wherein the first core particle and the second core particle furthercomprise a binder comprising one or more of plaster of Paris, flour,biodegradable bleached wheat flour, starch, colloidal silica, kaolin,bentonite, or gluten.
 7. The particulate fertilizer composition of claim1, wherein the first core particle and the second core particle furthercomprise a filler comprising one or more of silica, dried distillersgrains with solubles (DDGS), or rice husk.
 8. The particulate fertilizercomposition of claim 1, wherein the first core particle and the secondcore particle further comprise a pH buffering agent comprising one ormore of chalk powder, CaCO₃, MgO, KH₂PO₄, NaHCO₃, Na₂CO₃, or K₂CO₃. 9.The particulate fertilizer composition of claim 1, wherein theparticulate fertilizer composition comprises a plurality of firstparticles and a plurality of second particles, and wherein the weightratio of the first particles to the second particles is approximately1:1.
 10. The particulate fertilizer composition of claim 1, wherein thefirst core particle comprises 10 to 94 wt % binder, 0 to 60 wt % filler,5 to 60 wt % pH balancing agent, and 1 to 5 wt % NBTPT, and wherein thesecond core particle comprises 10 to 85 wt % binder, 0 to 50 wt %filler, 5 to 60 wt % pH balancing agent, and 10 to 50 wt % DCD.
 11. Theparticulate fertilizer composition of claim 1, wherein the weight ratioof the first shell to the first core particle and of the second shell tothe second core particle is between about 40:1 and 5:1.
 12. Theparticulate fertilizer composition of claim 1, wherein the first coreparticle and second core particle are between about 0.5 and 2 mm indiameter and wherein the first particle and the second particle arebetween about 1 and 8 mm in diameter.
 13. The particulate fertilizercomposition of claim 1, wherein the particulate fertilizer compositioncomprises nitrogen and less than 20 wt % of the nitrogen in theparticulate fertilizer composition is lost via ammonia volatilizationafter being exposed to Greenville soil or Crowley soil for 20 days. 14.A particulate fertilizer composition comprising at least two of thefollowing groups of particles: (a) a plurality of first particles, eachfirst particle comprising: (i) a first core particle comprisingN-(n-butyl) thiophosphoric triamide (NBTPT) and a binder; and (ii) aurea-containing fertilizer composition in contact with the outer surfaceof the first core particle; and (b) a plurality of second particles,each second particle comprising: (i) a second core particle comprisingdicyandiamide (DCD) and a binder; and (ii) a urea-containing fertilizercomposition in contact with the outer surface of the second coreparticle; and (c) a plurality of third particles, each third particlecomprising a urea-containing fertilizer and not comprising a coreparticle.
 15. The particulate fertilizer composition of claim 14,wherein each of the first particles are substantially free of anynitrification inhibitor, each of the second particles are substantiallyfree of any urease inhibitor, and each of the third particles aresubstantially free of any nitrification inhibitor or urease inhibitor.16. The particulate fertilizer composition of claim 14, wherein each ofthe third particles further comprise a nitrification inhibitor.
 17. Theparticulate fertilizer composition of claim 14, wherein theurea-containing fertilizer composition in contact with the outer surfaceof the second core particle further comprises DCD.
 18. The particulatefertilizer composition of claim 14, wherein the third particle has adiameter of at least 0.5 mm.
 19. The particulate fertilizer compositionof claim 14, wherein the particulate fertilizer composition comprises aplurality of the first particles and a plurality of the secondparticles, wherein the particulate fertilizer does not comprise thethird particle, and wherein the weight ratio of the first particles tothe second particles is approximately 1:1.
 20. The particulatefertilizer composition of claim 14, wherein the particulate fertilizercomposition comprises a plurality of the third particles and either aplurality of the first particles or a plurality of the second particles,and wherein the weight ratio of the third particles to the firstparticles or the second particles is approximately 1:1.